Immunology

Question 1

Innate immune system in the eye?

Answer 1

Eye doesn’t have skin and not many commensal bacteria
However to provide protection there is the blink reflex. Tears flush out the eye.
There are chemical properties of the tears which are antimicrobial e.g. lysozomes or anti-adhesive
There is also a mucous layer which is anti adhesive
There are immune cells in the eye: neutrophils, macrophages and conjunctival mast cells.

Question 2

What is the principle APC for the external eye?

Answer 2

Langerhans cell (specialised dendritic cells)

Question 3

Langerhans cells in the eye are rich in _______ and found in abundance in the _____

Answer 3

Class 2 MHC (this makes sense as class 2 is only present on APCs and the eye doesn't want to survey lots of non APCS as immune privileged)
Corneoscleral limbus

Question 4

What is the only part of the eye with lymphatic drainage?

Answer 4

The conjunctiva

Question 5

Why is the cornea and sclera described as a down regulated immune environment?

Answer 5

Avascularity
No lymphatics/lymphoid tissue
Relative lack of APCs
Langerhans cells only in peripheral cornea

Question 6

Describe how the lacrimal gland and drainage system contributes to the immune system of the eye?

Answer 6

Lacrimal gland:
More plasma cells (IgA) and CD8+ T cells compared to conjunctiva
T cells in small groups around intralobar ducts
Resting lymphoid cells very rarely observed

Lacrimal drainage system:
Diffuse lymphoid tissue and follicles (40-50%) in mucosa (MALT)

Question 7

What is the blood ocular barrier? What makes it up?

Answer 7

Choroid and retina together form the blood ocular barrier- series of tight junctions between cells forming a physical barrier between local blood vessels and many parts of the eye.

Question 8

Describe what is meant by immune privilege?

Answer 8

Certain places in the body that are able to tolerate the introduction of antigens without eliciting an inflammatory immune response.

Question 9

What areas in the body have immune privilege?

Answer 9

Brain and CNS debated, definitely in testes, placenta/fetus and eyes

Question 10

What areas in the eye have immune privilege?

Answer 10

cornea, anterior chamber, lens, vitreous cavity, subretinal space

Question 11

Why does corneal graft rejection not occur very often?

Answer 11

Immune privilege in the eye

Question 12

Type 1 hypersensitivity is ____
Mediated by _____
Eye example is ______

Answer 12

Immediate allergy
IgE
Acute allergic conjunctivitis

Question 13

Type 2 hypersensitivity is ____
Mediated by _____
Eye example is ______

Answer 13

Direct cell killing
Antibodies
Ocular cicatricial pemphigoid

Question 14

Type 3 hypersensitivity is ____
Mediated by _____
Eye example is ______

Answer 14

Immune complex mediated
Complement system
Autoimmune corneal melting (may be caused by RA or lupus)

Question 15

Type 4 hypersensitivity is ____
Mediated by _____
Eye example is ______

Answer 15

Delayed hypersensitivity
T cells and macrophages
Corneal graft rejection

Question 16

Describe 3 mechanisms that downregulate the immune response in the eye?

Answer 16

• SEPARATION: Immunological ignorance
• Corneal cells have ↓ expression of MHC Class I molecules and do not express MHC Class II molecules
• Normal cornea lacks blood and lymphatic vessels
• INHIBITION: Development of an intraocular immunosuppressive microenvironment
• Local factors within the eye inhibit components of the immune response to reinforce the protection provided by immune privilege
• REGULATION: Peripheral tolerance to ocular antigens
• ACAID
The eye is ignorant to induction of non-self, the body is tolerant to the presence of ocular antigens, and the local environment within the eye supports these.

Question 17

Describe Anterior chamber associated immune deviation?

Answer 17

The placement of foreign antigen into the ocular microenvironment can induce a systemic form of tolerance to the foreign antigen = ACAID
‘Peripheral tolerance’ to ocular antigens
ACAID protects the eye and visual axis from the collateral damage of an immune response to infection by suppressing a future potentially damaging response to infection.